`HC-=CH+Hxoverset("dark")toXunderset(HX)overset(dark)toY`. Find X&Y.
A. `CH_(2)=CH_(2)&overset(X)overset(|)(C)H_(2)-overset(X)overset(|)(C)H_(2)`
B. `CH_(2)=CHX&CH_(3)-CHX_(2)`
C. `CH_(2)=CHX&overset(X)overset(|)(C)H_(2)-overset(X)overset(|)(C)H_(2)`
D. `CH_(2)=CHX&X_(2)CH-CHX_(2)`
